The present invention relates generally to contact lenses, and more particularly, to a corneal contact lens unit which includes a specifically designed and shaped, fused-in-place bifocal segment.
The present invention is directed toward a bifocal contact lens which is based on sound optical principles, but which is designed to allow greater latitude in fitting without sacrificing both desirable characteristics of both distant vision and near vision.
Bifocal contact lenses are well known in the art. The earliest bifocal contact lenses were those in which the bifocal segments were designed to shapes or configurations which were the same as their counterparts found in spectacle bifocals. These included the type wherein the upper surface of the bifocal segment was a straight, horizontally extending line, or an upwardly directed arcuate convex line or surface. Other bifocal segments in contact lenses included the fully circular segment, which provides a bifocal or close vision zone completely surrounding the distant vision or central portion of the lens.
Another type of bifocal contact lens which is now in general use is a bifocal lens wherein the upper surface of the bifocal segment appears in front elevation as a slight curve or crescent configuration, with the center portion of the segment being lower than the outer edges thereof when the lens is in a position of use on the wearer. This configuration of segment is probably the most popular one in use today.
As shown in U.S. Pat. No. 3,684,357, there are also bifocal segments of the type which incorporate a compound or so-called bi-curved upper surface shape, that is, an upper surface having a curvilinear central portion of a first radius, and outer edge portions extending outwardly and upwardly therefrom in a curve of much larger radius. The upper segment line thus appears as a downwardly extending, larger radius arc having a central portion extending further therebeneath and characterized by a much smaller radius.
In certain bifocal applications, it is desired to arrange the bifocal contact lens so that distant vision is obtained by the viewer when looking straight ahead or slightly downwardly, and so that near vision is provided as the user casts his eyes more sharply downwardly. Certain contact lens users, including draftsmen, typists, and others who customarily use left-to-right eye movements in their work, desire a bifocal contact lens wherein the user may look through the bifocal segment when looking laterally and slightly downwardly, as well as when looking downwardly only. The type of bifocal segment described in U.S. Pat. No. 3,684,357 shows such a segment. The present invention represents an improvement over the type of bifocal segment described and claimed in such patent, and is intended to provide greater convenience in use for the user, increased usable reading fields on both downward and down-and-lateral vision, and other advantages as well.
In view of the shortcomings of known prior art lenses, it is an object of the present invention to provide an improved fused bifocal corneal contact lens.
Another object is to provide a bifocal contact lens having a bifocal segment of a novel configuration which is used in a fused or one-piece bifocal contact lens unit.
Still another object is to provide a contact lens which allows greater latitude in fitting without sacrificing either distant or near vision capabilities.
A still further object is to provide a bifocal contact lens which may be made by known methods, but which is free of the drawbacks associated with even the most advantageous prior art bifocal lenses.
Still another object of the present invention is to provide a bifocal contact lens having a bifocal segment designed to permit the use of less prism in the lens and which is more tolerant to rotation from the horizontal axis without loss of the wearer's ability to view objects through the segment for close vision.
A still further object is to provide a segment design which provides the maximum distance field in the lens consistent with a largely increased reading field which is usable by the viewer without the drawbacks associated with prior art lenses.
Another object is to provide a bifocal contact lens having a reading field which is disposed in use very close to the visual axis and which is thus accessible to the viewer without exaggerated eye movements.
A still further object is to provide a lens which provides the advantages of the convenience of a good bifocal contact lens and which maintains these advantages even if fit somewhat loosely by the practitioner (the person fitting the lens to the user). A still further object is to provide a lens in which the extremities of the bifocal segment do not cut across the visual axis even if the lens is fitted so loosely as to permit undue ease of rotation on the eye, or if the lens rotates somewhat for any reason.
A still further object is to provide a fused bifocal contact lens having a near vision segment which includes an upper segment surface or line or surface having a central portion of an arcuate shape and lateral portions extending outwardly and downwardly from the point at which the upper segment line meets the circular portion thereof.
The foregoing objects and advantages are achieved by providing a bifocal contact lens which includes a bifocal segment having an upper bi-curve segment surface defined by a radially inner, partially circular first element and by outwardly and slightly downwardly extending second and third elements extending between the ends of the inner surface and the outer surface of the segment, with the ends of the inner surface lying below the center of the lens.
The exact manner in which these and other objects and advantages are achieved in practice will become more clearly apparent when reference is made to the foregoing detailed description of the preferred embodiments of the invention set forth by way of example and shown in the accompanying drawings, in which like reference characters indicate corresponding parts throughout.